Beneficiated fiber and composite

ABSTRACT

A beneficiated fiber and composite including a fiber having a lumen with voids. A suspension including a bonding agent, chemical blowing agent, and catalyst is drawn into the lumen by a capillary action to beneficiate the fiber. The beneficiated fiber may be imbedded with a polymeric material to form the composite. The natural voids of the lumen are preserved by the suspension causing the fiber to maintain natural density and strength characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.10/684,117, filed Oct. 10, 2003, now U.S. Pat. No. 7,175,907, whichclaims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) ofapplication Ser. No. 10/269,051, filed Oct. 10, 2002, now abandoned.

FIELD OF THE INVENTION

The invention relates to fiber composites and a manufacturing methodthereof. More specifically, the invention relates to a beneficiatedcellulose fiber for use in a plastic composite and a manufacturingmethod thereof.

BACKGROUND OF THE INVENTION

In response to the increased cost and diminishing quality andavailability of natural wood, composites consisting essentially ofplastic and natural fibers are steadily replacing the use of traditionalwood in construction and transportation applications. Unlike naturalwood that splinters and warps, the composites are weather resistant andrelatively maintenance free but still offer the same look and feel asnatural wood.

The composites typically comprise a plurality of fibers imbedded in apolymeric material. The polymeric material typically consists of a highor low-density olefin thermoplastic or a vinyl based thermoplasticpolymer depending on the desired end-use characteristics of thecomposite. The fibers may be chosen from a variety of plants dependingon the desired characteristics of the fiber, for example, density orstrength. The natural variation in the apparent density of the differentplant fibers is attributable to the presence of a central void or lumenwithin the fiber.

The manufacture of the composite typically involves extruding of thepolymeric material and the fiber. During the manufacture thereof, anextruder melts the polymeric material and mixes the melted polymericmaterial with the fiber. As a result of the mixing, the melted polymericmaterial becomes imbedded with the fiber. A bonding agent may be addedto the mixture to aid in achieving an adhesive bond between the fiberand the polymeric material. Many other “additives” may be introduced,such as, stabilizers, antioxidants, UV absorbers, fillers and extenders,pigments, process aids and lubricants, impact modifiers, bactericidesand other materials that enhance physical and/or chemical properties aswell as processing. A chemical blowing agent or gas may also beintroduced into the mixture. While in the extruder, the blowing agentdecomposes, disbursing a gas, such as, nitrogen or carbon dioxide, intothe melted polymeric material. After the polymeric material, fiber andother additives are mixed, the melted mixture exits the extruder througha die. As the polymeric material exits the die, the extrusion pressureis reduced to atmosphere and the polymeric material begins to coolcausing the entrained gases to expand as bubbles within the meltedmixture. The bubbles are trapped by the surrounding polymeric materialand form voids in the composite. These voids reduce the overall densityand weight of the composite.

Often during extrusion, the lumen in the fiber collapses undercompressive pressure. When the lumen collapses the natural voids in thefiber are lost causing the natural density of the fiber to increase.Because the density of the fiber is increased, the mass of the compositealso increases. This increased density runs counter to the advantages ofusing fiber, which is mass reduction and stiffness enhancement.

It is therefore desirable to develop a fiber and a method of manufacturethereof wherein the lumen does not compress during extrusion such thatthe natural voids of the lumen are preserved causing the fiber tomaintain natural density and strength characteristics. It is alsodesirable to reduce the overall composite mass by using a blowing agentto further introduce void volume within the polymeric material.

SUMMARY OF THE INVENTION

The invention relates to a beneficiated fiber and composite. Thebeneficiated fiber includes a fiber having a lumen with voids. Asuspension is drawn into the lumen to beneficiate the fiber. A polymericmaterial is imbedded with the fiber to form the composite. The naturalvoids of the lumen are preserved by the suspension ingredients allowingthe fiber to maintain natural density and strength characteristics.

The invention further relates to a method for manufacturing abeneficiated fiber. A fiber is mixed with a suspension to form ahomogeneous mixture. The suspension is drawn into a lumen of the fiberby capillary action to beneficiate the fiber and the beneficiated fiberis cooled. The beneficiated fiber may then be mixed with a meltedpolymeric material to form a composite that is extruded to form acomposite structural member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a beneficiated fiber compositestructural member.

FIG. 2 is a perspective view of a bundle of fibers.

FIG. 3 is a flow diagram showing the process of beneficiating the fibersand manufacturing a beneficiated fiber composite.

DETAILED DESCRIPTION OF THE INVENTION

The invention will first be described generally with reference to FIG.1, which shows a beneficiated fiber composite structural member 10. Thecomposite structural member 10 has a plurality of fibers 12 beneficiatedwith a suspension 14 and imbedded with a polymeric material 16. Thesuspension 14 may consist of a chemical blowing agent or foaming agent,a catalyst, and a carrier. The composite structural member 10 also has aplurality of voids 18. The major components of the composite structuralmember 10, and the method of beneficiating the fiber 12 andmanufacturing the composite structural member 10 will hereafter bedescribed.

Each of the major components of the composite structural member 10 willnow be described in greater detail. FIG. 2 shows the fiber 12. The fiber12 may be a natural fiber from a bast fiber plant, such as, flax, hemp,jute, coir, kenaf, or ramie, or alternatively may be refined wood,wheat, straw, or other ligno-cellulosic fibers. The bast fiber plantsare characterized by their long, strong fiber bundles and high cellulosecontent. The fibers 12 from the bast fiber plants have a high tensilestrength and a relatively low apparent density of 0.28-0.62 g/cc,yielding an especially high strength to weight ratio. Each fiber 12 hasa central void or lumen 20. The lumen 20 has an opening of approximately30 microns. Other fibers having a high purity and a high aspect ratio(ratio of fiber diameter to length) may also be used, such as, refinedwood, wheat, straw, or other ligno-cellulosic fibers.

The suspension 14 may include a chemical blowing agent or foaming agent,a catalyst, and a carrier. The individual components are combined andthen agitated or emulsified to form a blended mixture. The carrier maybe an acrylic urethane polymer solution or emulsion, but other knownfilm-forming polymers may be used to strengthen the internal walls ofthe fiber. Examples of polymer networks useful to this end result areacrylics, epoxies, phenolics, melamines, vinyls, as well as virtuallyall film-forming thermoset or thermoplastic polymers. The carriers maybe as emulsions with water or as solutions where the blowing agentand/or the catalysts are dispersed therein. The chemical blowing agentor foaming agent may be any of a variety of known chemicals thatreleases a gas upon thermal decomposition. Exothermic blowing agents aresuitable chemical blowing agents. For example, such blowing agents mayinclude a very fine grade of azodicarbonamide or a hydrazine derivativesuch as benzenesulfonyl hydrazide. The catalyst or activator may be acalcium carbonate. Other examples of particulate catalysts or activatorsmay be selected compounds of cadmium, zinc, barium, calcium, strontium,magnesium, lead, tin or silicon. Any known catalyst or activator may beused that assists in the decomposition of the blowing agent. Because thelumen 20 of the fiber 12 has an approximate opening of 30 microns,particulate ingredients should be no greater than 5 microns. Thedispersion of the blowing agent and the other particulates require highvelocity dispersators to deagglomerate the particles. Any knowndispersator may be used for this process, such as, Cowles and Hockmeyerdispersators.

The polymeric material 16 may be a polyvinyl chloride foam, however, anyof a variety of thermoplastic polymers may be used, such as: polyolefinsincluding but not limited to polyethylene, and polypropylene;cellulosics, other vinyls, acrylics, urethanes, styrenics etc. Thecomposite structural member 10 preferably includes about 25-99% of thepolymeric material 16.

A coloring agent, such as colored pigments, etc., may also be added tothe polymeric material 16 or adsorbed onto an exterior surface of thefiber 12 to obtain a desired color. Stabilizers, antioxidants, fillersand extenders, wetting agents, bonding agents, impact modifiers as wellas process aids may also be selectively adsorbed onto the exteriorsurface of the fiber 12. These additives are generally added to thepolymeric material 16 prior to or during extrusion, but adsorbing theseadditives onto the surface of the fiber 12 prior to extrusion providesan improved vehicle for introduction of these additives into thecomposite structural member 10. These additives are individuallyselected to enhance performance and or processing within the polymericmaterial 16.

A method of beneficiating the fibers 12 and manufacturing the compositestructural member 10 will now be described in greater detail withreference to FIG. 3.

The method of beneficiating the fibers 12 is shown in the first portionof the process labeled “A” in FIG. 3. In order to beneficiate the fibers12, beginning at step 22, the fibers 12 are positioned onto a screw of acontinuous kneader/mixer designed to progressively knead and mix drymaterials with liquid materials on a continuous basis. The continuouskneader/mixer has a screw and kneading element design that does not cut,but rather only opens bundles of the fiber 12 to ensure the requiredaspect ratio (ratio of fiber diameter to length). The preferred deviceis a Readco Continuous Processor, however, it will be appreciated andunderstood by those skilled in the art that many other single ortwin-screw kneader/mixers may be used to achieve substantially similarresults.

At step 24, the suspension 14 is positioned in a holding container thatfeeds the suspension 14 into the kneader/mixer. A metering pump capableof handing viscous liquids and emulsified materials is required. It isimportant that nothing breaks the emulsion or agglomerates the suspendedparticles. The suspension 14 is then added to the fibers 12 and kneadedwith the fibers 12, as shown at step 26. The suspension 14 may rangefrom approximately 1-10 parts to approximately 100 parts of the fiber 12to produce a homogeneous mixture. Temperatures in the kneader/mixerduring the step 26 range from 200-350 degrees Fahrenheit. Care needs tobe taken to assure even kneading and mixing at step 26. As the fiber 12is kneaded with the suspension 14, capillary action draws the suspensioninto the lumen 20 of the fiber 12 where it is absorbed by the fiber 12.The suspension 14 thereby beneficiates the fiber 12 and preserves thelumen 20 for later processing in the extruder at step 32.

The adsorption of the other additives that are deposited onto thesurface of the fiber 12 takes place after step 26. In step 28, otheradditives are added as liquid concentrates or dry mixtures to thekneader/mixer. These additives are mixed and dispersed so as to beevenly deposited onto the surface of the fiber 12. Exterior heat ofapproximately 350-500 degrees Fahrenheit is contained on the barrel ofthe kneader/mixer so that the additives and the fiber 12 are bettermixed and process volatiles are removed. Care should be taken so thatthe temperature of the additives are maintained at temperature which isbelow the activation temperature of the selected chemical blowing agent.The beneficiated fiber 12 exits the kneader/mixer and is introduced intoa continuous ribbon blender, which cools and fluffs the fiber, as shownat step 30.

The method of manufacturing the composite structural member 10 is shownin the second portion of the process labeled “B” in FIG. 3. Thecomposite structural member 10 is formed by positioning the beneficiatedfiber 12 in an extruder at step 32 with the polymeric material 16. Theextruder at step 28 melts the polymeric material 16 and mixes thepolymeric material 16 with the beneficiated fiber 12. As a result of themixing, the polymeric material 16 coats the beneficiated fiber 12 andbecomes imbedded with the suspension 14. As an alternative to extrusion,the beneficiated fiber 12 and polymeric material 16 may be heated, mixedand injection molded into a mold. The heat used to melt the polymericmaterial 16 further causes the blowing agent in the lumen 20 todecompose. The blowing agent decomposes at a prescribed temperaturegoverned by the catalyst. As the blowing agent decomposes, the blowingagent disperses a gas, such as, nitrogen or carbon dioxide that formsbubbles in the melted polymeric material 16. Because the lumen 20 of thebeneficiated fiber 12 is adequately filled with the ingredients of thesuspension 14, the lumen 20 is preserved during extrusion to maintainthe natural density of the fiber 12.

The melted mixture of the beneficiated fiber 12 and the polymericmaterial 16 passes through a die to exit the extruder at step 34 in theform of a sheet or any other extrudable section. As the melted mixtureexits the die, the melted mixture begins to cool causing the gas toexperience a pressure drop that expands the bubbles trapped by thesurrounding polymeric material 16 to form the voids 18. The meltedmixture may be extruded in any of a variety of pre-determined shapes asit exits the die or the melted mixture may be molded. As an optionalalternative, the extrusion may be thermoformed into a variety of shapes.The cooled melted mixture forms the composite structural member 10.

Because the lumen 20 does not compress during extrusion, the naturalvoids of the lumen 20 are preserved by the suspension 14 causing thefiber 12 to maintain natural density and strength characteristics. Thecomposite structural member 10, therefore, is lightweight and hasexceptional strength. The composite structural member 10 is suitable foruse in any of a variety of semi-structural applications including, butnot limited to, decking, exterior trim profiles, window profiles,railing, gazebos, cladding, siding, moulding, and door jambs, etc.

It should be understood by those reasonably skilled in the art that thefirst portion “A” of the manufacturing process in FIG. 3 can becompleted at a manufacturer's location while the second portion “B” ofthe manufacturing process may be completed at a point of service or acustomer location where composite structural members 10 are formed.Since the second portion “B” of the process only requires standardextruding equipment, the beneficiated fiber 12 may be screened,classified, and packaged, and then, supplied to the customer after step30. The customer may then manufacture the composite structural members10 at its location. Optionally, the entire process including bothportions “A” and “B,” may be completed at the manufacturer's locationaccording to customer specifications. Where the second portion of theprocess “B” is conducted at the point of service or customer location,the customer has ultimate flexibility in determining the desiredpolymeric ratio, color, and shape of the composite structural member 10among other characteristics.

The foregoing illustrates some of the possibilities for practicing theinvention. Many other embodiments are possible within the scope andspirit of the invention. It is, therefore, intended that the foregoingdescription be regarded as illustrative rather than limiting, and thatthe scope of the invention is given by the appended claims together withtheir full range of equivalents.

1. A composite comprising: a fiber having a lumen with voids; asuspension drawn into the lumen to beneficiate the fiber, the suspensionincluding a chemical blowing agent; and a polymeric material imbeddedwith the fiber; whereby the natural voids of the lumen are preserved bythe suspension causing the fiber to maintain natural density andstrength characteristics.
 2. The composite of claim 1 wherein thechemical blowing agent is exothermic.
 3. The composite of claim 2wherein the chemical blowing agent is azodicarbonamide.
 4. The compositeof claim 2 wherein the chemical blowing agent is a hydrazine derivative.5. The composite of claim 1 wherein the suspension includes a carrier.6. The composite of claim 5 wherein the carrier is a polymer networkselected from the group of acrylics, epoxies, phenolics, melamines andvinyls.
 7. The composite of claim 5 wherein the carrier is afilm-forming thermosetting polymer.
 8. The composite of claim 1 whereinthe suspension includes a catalyst.
 9. The composite of claim 8 whereinthe catalyst is selected from the group of calcium carbonate, andcompounds of cadmium, zinc, barium, calcium, strontium, magnesium, lead,tin or silicon.
 10. The composite of claim 1 wherein approximately 1-10parts of the suspension are mixed with approximately 100 parts of thefiber.
 11. The composite of claim 1 wherein the fiber is a bast fiber.12. The composite of claim 11 wherein the fiber is flax.
 13. Thecomposite of claim 11 wherein the fiber is hemp.
 14. The composite ofclaim 11 wherein the fiber is jute.
 15. The composite of claim 11wherein the fiber is coir.
 16. The composite of claim 11 wherein thefiber is kenaf.
 17. The composite of claim 11 wherein the fiber isramie.
 18. The composite of claim 1 wherein the fiber is a wood fiber.19. The composite of claim 1 wherein the fiber is a wheat fiber.
 20. Thecomposite of claim 1 wherein the fiber is a straw fiber.
 21. Thecomposite of claim 1 wherein the fiber is a ligno-cellulosic fiber. 22.The composite of claim 1 comprising approximately 25% to 99% of thepolymeric material.
 23. The composite of claim 22 wherein the polymericmaterial is a polyvinyl chloride foam.
 24. The composite of claim 22wherein the polymeric material is a polyolefin.
 25. The composite ofclaim 24 wherein the polymeric material is polyethylene.
 26. Thecomposite of claim 24 wherein the polymeric material is polypropylene.27. The composite of claim 22 wherein the polymeric material is acellulosic.
 28. The composite of claim 22 wherein the polymeric materialis a vinyl.
 29. The composite of claim 22 wherein the polymeric materialis an acrylic.
 30. The composite of claim 22 wherein the polymericmaterial is a urethane.
 31. The composite of claim 22 wherein thepolymeric material is a styrenic.
 32. The composite of claim 1 furthercomprising at least one additive that is adsorbed onto a surface of thefiber.
 33. The composite of claim 32 wherein the least one additive thatis a coloring agent.
 34. The composite of claim 32 wherein the least oneadditive that is a stabilizer.
 35. The composite of claim 32 wherein theleast one additive that is an antioxidant.
 36. The composite of claim 32wherein the least one additive that is a filler.
 37. The composite ofclaim 32 wherein the least one additive that is an extender.
 38. Thecomposite of claim 32 wherein the least one additive that is a wettingagent.
 39. The composite of claim 32 wherein the least one additive thatis a bonding agent.
 40. The composite of claim 32 wherein the least oneadditive that is an impact modifier.
 41. The composite of claim 1wherein the composite is formed into a composite structural member. 42.The composite of claim 41 wherein the composite structural member is adecking board.
 43. The composite of claim 41 wherein the compositestructural member is an exterior trim profile.
 44. The composite ofclaim 41 wherein the composite structural member is a railing.
 45. Thecomposite of claim 41 wherein the composite structural member is agazebo component.
 46. The composite of claim 41 wherein the compositestructural member is a cladding member.
 47. The composite of claim 41wherein the composite structural member is a molding.
 48. The compositeof claim 41 wherein the composite structural member is a door jamb. 49.The composite of claim 41 wherein the composite structural member is asiding member.
 50. The composite of claim 41 wherein the compositestructural member is a window profile.
 51. The composite of claim 41wherein the composite structural member is formed by extruding thecomposite.
 52. The composite of claim 51 wherein the compositestructural member is further formed by thermoforming.
 53. The compositeof claim 41 wherein the composite structural member is formed byinjection molding.